The present invention is directed to apparatuses and methods for driving write heads in memory devices, and especially to write driver apparatuses and methods providing symmetry in drive signals.
The construction of read/write heads in memory devices, such as hard disk drive units, commonly situates electrical lines providing signals to the write head (i.e., write lines) in close proximity with electrical lines carrying read signals from the read head (i.e., read lines). Write lines are generally provided in pairs in order to provide fully differential write signaling to the write head. Similarly, read lines are generally provided in pairs in order to provide fully differential signaling from the read head.
When signals provided to a write head on two write lines are not symmetric there can be a pulse induced on the adjacent read lines. Such a pulse on the read lines can create an overvoltage condition on the read head that can result in burnout of the read head. This problem has been addressed in the past by treating the symptom—the pulse induced in the read lines—rather than dealing with the cause—asymmetric signals on the write lines. For example, one solution has been to turn off bias signals to the read head while performing a write operation. This avoided adding the induced pulse to the read bias signal and therefore reduced the likelihood of an overvoltage condition in the read head. Another prior art solution was to simply place the write lines and the read lines further apart, thereby limiting signal levels that may be induced on the read lines by asymmetry in write signals.
The prior art solutions' addressing the symptom (i.e., pulses induced on the read lines) rather than the cause (i.e., asymmetry in the write signals) became less effective as the size of the memory devices shrank. Another cause of reduced effectiveness of the prior art solutions was the increasing the capacity of storage in disc storage devices that resulted in denser storage of data. Sensitivity of read heads necessarily followed higher data storage density in order that the read head could distinguish among individual data units closely situated on a disc because of the denser storage of data on the disc.
Symmetric signals on write lines assure no pulse is induced on nearby read lines. Symmetry requires complementary signaling in the differential signaling provided to a write head. That is, each signal must be equal in magnitude and opposite in polarity to assure an algebraic zero in total effect of the signals on nearby read lines. Said another way, each of the two differential signals provided to the write lines must be a mirror image of the other signal; the signals must be complementary signals.
There is a need for an apparatus and method for driving a write head that provides complementary signals to write lines in a disk storage device.